Attach error nodes to network tree

[Aptimex]

Currently nodes with errors are displayed in their own separate box in the status command. However, in some cases (probably just leaf servers) we might be able to pull together enough information to attach them to the correct spot in the network tree.

Excerpt from the discussion here: #57 (comment)

...could we use the Endpoint field of a failed node (which is known from the start, by client config alone) to walk the tree through the responsive nodes based on routes?

Basically walk the routing algorithm. Follow the Endpoint address through the relay nodes' AllowedIPs.

I think there's still a problem in that once you get to the first failed node, we lose the structure of all nodes behind it, but that's not too terrible of a downside.